The entire contents of Japanese Patent Application No. 8-338490 filed on Dec. 12, 1996 are incorporated herein by reference.
This invention relates to a distributed control network system involving the use of an object-oriented language designed for Internet such as Java.
A known distributed control network system as illustrated in FIG. 1 of the accompanying drawings typically comprises individual control networks (local control networks 9, 15) connected thereto by way of local control servers 7, 13 in addition to a control client 3 and a global control server 5 connected by way of a TCP/IP, which is an Internet protocol. Then, individual control nodes 11, 17 comprising non-proprietary distributed control chips are connected to the local control networks 9, 15.
To date, while controls can be interchanged among the control nodes within a local control network of a distributed control network system, no interchange of controls is possible among control nodes connected to different local control networks. For example, the control node 11 connected to the local control network 9 cannot control the control node 17 connected to the local control network 15 (and the control node 17 requires a specific program adapted to its environment for program execution).
Thus, the processing operations of each control node have to be described and compiled to produce object codes in order to prepare an execution file by combining the object codes by means of linkers.
Known distributed object communication techniques include RPC (Remote Procedure Call). The RPC is a basic technique for realizing distributed processings designed to call a procedure (program) for operating on a different computer connected to the network. "Java", an object-oriented language for Internet, comprises RMI (Remote Method Invocation) as a distributed object communication feature. However, all of these techniques are designed for synchronous calls and the client calling the server is held in a stand-by state from the time it calls the server to the time the latter responds so that the client can proceed only after the server responds. Such an arrangement is not adapted to control networks because they are typically designed in such a way that a program operates in response to an event to generate another event and another program operates in response to the latter event and so on.
Meanwhile, "socket" is known as a typical inter-program communication technique of UNIX. However, with the "socket", the data format to be used for exchanging programs between a program asking for a processing operation and a program asked for carrying out the processing operation has to be rigorously defined in the first place and then the programs have to be written according to the defined format. Therefore, the programmer cannot write a program to be asked for carrying out a processing operation without thoroughly understanding the processing procedure of the program. Additionally, the "socket" is basically a 1 to 1 inter-program communication technique.
As described above, to date, control nodes connected to different control networks of a distributed control network system cannot communicate with each other.
Additionally, known inter-program communication techniques including RPC and RMI are not adapted to control networks because they are designed for synchronous calls. Still additionally, the "socket" does not have a standardized data format and is basically a 1 to 1 inter-program communication technique and hence it is not adapted to control networks.
Finally, while various program developing tools using object-oriented languages are known, they are not adapted to the GUI (Graphical User Interface) environment and hence accompanied by difficulties for preparing programs. For instance, when a user uses various tools, he or she must input individual tool's name one by one, resulting in cumbersome. Thus, there has been a strong demand for a powerful tool that facilitates the operation of developing programs.